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United States Patent |
5,222,483
|
Plisek
|
June 29, 1993
|
Acoustic pressure pulse generator
Abstract
An acoustic pressure pulse generator has a pressure pulse source in the
form of a concussively driveable membrane, the membrane limiting a volume
within the generator which contains a liquid acoustic propagation medium,
the generator also having a wall therein spaced from the membrane, the
wall dividing the volume into two sub-volumes. The acoustic propagation
medium is circulated through an inlet in one of the sub-volumes and an
outlet in the other sub-volume, with the two sub-volumes being in fluid
communication via a flow restrictor through which the acoustic propagation
medium flows. The restrictive effect of the flow restrictor is dimensioned
so that the acoustic propagation medium contained in the sub-volume
between the wall and the membrane is maintained at a pressure for
effecting return of the membrane to its initial position after the
membrane has been concussively driven.
Inventors:
|
Plisek; Franz (Erlangen, DE)
|
Assignee:
|
Siemens Aktiengesellschaft (Munich, DE)
|
Appl. No.:
|
877710 |
Filed:
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May 4, 1992 |
Foreign Application Priority Data
Current U.S. Class: |
601/4 |
Intern'l Class: |
A61B 017/22 |
Field of Search: |
128/660.03,24 EL
606/127-128
|
References Cited
U.S. Patent Documents
4530358 | Jul., 1985 | Forssman et al. | 128/24.
|
4669472 | Jun., 1987 | Eisenmenger.
| |
4674505 | Jun., 1987 | Pauli et al.
| |
4697588 | Oct., 1987 | Reichenberger.
| |
4715376 | Dec., 1987 | Nowacki et al. | 367/147.
|
4840166 | Jun., 1989 | Naser et al. | 128/24.
|
4879993 | Nov., 1989 | Reichenberger et al. | 128/24.
|
4928672 | May., 1990 | Grasser et al. | 128/24.
|
4977888 | Dec., 1990 | Rietter et al.
| |
5031626 | Jul., 1991 | Hassler et al. | 128/660.
|
5046483 | Sep., 1991 | Ogura | 128/24.
|
5095907 | Mar., 1992 | Kudo et al. | 128/24.
|
Foreign Patent Documents |
0131653 | Jan., 1985 | EP.
| |
0196353 | Oct., 1986 | EP.
| |
0242565 | Oct., 1987 | EP.
| |
3312014 | Oct., 1984 | DE.
| |
3525641 | Jan., 1987 | DE.
| |
3536073 | Apr., 1987 | DE.
| |
3605277 | Aug., 1987 | DE.
| |
8809252 | Dec., 1989 | DE.
| |
3835318 | Jun., 1990 | DE.
| |
9005596 | Aug., 1990 | DE.
| |
3926380 | Feb., 1991 | DE.
| |
Primary Examiner: Jaworski; Francis
Attorney, Agent or Firm: Hill, Steadman & Simpson
Claims
I claim as my invention:
1. A pressure pulse generator comprising:
a housing having a volume containing an acoustic propagation medium;
a pressure pulse source in said housing including a membrane limiting said
volume and means for concussively driving said membrane for causing said
membrane to interact with said acoustic propagation medium to generate an
acoustic pressure pulse therein;
rigid divider means separating said volume into first and second
sub-volume;
an inlet in fluid communication with one of said sub-volumes and an outlet
in fluid communication with the other of said sub-volumes and means for
circulating said acoustic propagation medium through said inlet and said
outlet; and
flow restrictor means placing said sub-volumes in fluid comminication for
restricting flow of said acoustic propagation medium from one sub-volume
to the other for maintaining a static pressure in the sub-volume disposed
between said divider means and said membrane for effecting return of said
membrane to an initial position after said membrane has been concussively
driven.
2. A pressure pulse generator as claimed in claim 1 further comprising
means for cooling said acoustic propagation medium as said acoustic
propagation medium flows from said outlet to said inlet.
3. A pressure pulse generator as claimed in claim 1 further comprising
means for degasifying said acoustic propagation medium as said acoustic
propagation medium flows from said outlet to said inlet.
4. A pressure pulse generator as claimed in claim 1 further comprising
means for varying the restrictive effect of said flow restrictor.
5. A pressure pulse generator as claimed in claim 1 wherein said inlet is
disposed for discharging said acoustic propagation medium into said
sub-volume disposed between said divider means and said membrane.
6. A pressure pulse generator as claimed in claim 1 wherein said flow
restrictor means is formed by at least one hole in said divider means.
7. A pressure pulse generator as claimed in claim 1 wherein said flow
restrictor is formed by a gap between said divider means and a neighboring
part.
8. A pressure pulse generator as claimed in claim 1 wherein said divider
means is shaped as an acoustic lens.
9. A pressure pulse generator as claimed in claim 1 wherein said membrane
consists of electrically conductive material and wherein said pressure
pulse source includes an electrical coil disposed opposite a side of said
membrane facing away from said acoustic propagation medium, and means
electrically connected to said coil for driving said membrane.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to a pressure pulse generator of the type
having a pressure pulse source which creates acoustic pressure pulses in a
liquid acoustic propagation medium by means of a concussively driveable
membrane, also known as an electrodynamic pressure pulse generator.
2. Description of the Prior Art
Electrodynamic pressure pulse generators are used for a large variety of
purposes. For example, such pressure pulse generators are used for medical
purposes to non-invasively disintegrate calculi in the body of a patient,
or to non-invasively treat pathological tissue conditions. For the first
purpose, positive pressure pulses (greater than atmospheric pressure) are
used, and in the latter application, negative pressure pulses (less than
atmospheric pressure) are preferably used. Such pressure pulse generators,
for example, may also be used in materials testing to charge material
specimens with pressure pulses.
The pressure pulse generator is always acoustically coupled in a suitable
manner to the subject to be acoustically irradiated, so that the pressure
pulses generated in the acoustic propagation medium can be introduced into
the subject with a minimum of reflections and energy loss. The pressure
pulse generator and the subject to be acoustically irradiated must
therefore be aligned relative to each other so that the region of the
subject to be acoustically irradiated is located in the propagation path
of the pressure pulses. If the pressure pulse generator is of the type
which produces focused pressure pulses, it must also be assured that the
region of the subject to be acoustically irradiated is located in the
focal region of the focused pressure pulses.
A pressure pulse generator of this type is described in U.S. Pat. No.
4,674,505. This pressure pulse generator is a so-called electromagnetic
shockwave generator which generates positive pressure pulses. This is
accomplished by supplying high-voltage pulses to an electrically
conductive coil arrangement, thereby causing the rapid build-up of a
magnetic field. An electrically conductive membrane is disposed opposite
the coil arrangement, and this magnetic field induces a current in the
membrane in an opposite direction to the current flowing in the coil
arrangement. The membrane current also is accompanied by a magnetic field,
which is opposite in direction to the magnetic field associated with the
coil arrangement. Repulsion forces are thereby rapidly produced, causing
the membrane to be concussively moved rapidly away from the coil
arrangement. The membrane interacts with an acoustic propagation medium to
produce a pressure pulse therein, which gradually intensifies to form a
shockwave along its propagation path.
A problem in pressure pulse generators of this type is that the membrane
must be returned to its initial position after a pressure pulse has been
generated. Only by doing so is it insured that the membrane will assume a
defined position initial position before generating a further pressure
pulse. It is important that the membrane assume such a defined initial
position in order for successively generated shockwaves to coincide with
sufficient precision with respect to their acoustic characteristics. A
pressure pulse generator is disclosed by European Application 0 188 750,
corresponding to U.S. Pat. No. 4,697,588 wherein return of the membrane to
its initial position is accomplished by charging that side of the membrane
facing away from the acoustic propagation medium with an under-pressure.
Although the membrane is reliably returned to its initial position by this
approach, a rather substantial design outlay is required and an
under-pressure (suction) source must be provided.
A pressure pulse generator of the type described above is also disclosed in
German OS 34 43 295, corresponding to U.S. Pat. No. 4,669,472, wherein the
membrane is returned to its initial position by the acoustic propagation
medium, which is maintained at a static pressure sufficient to accomplish
this result. This approach has the disadvantage that the acoustic
propagation medium adjacent the membrane cannot be conducted through a
degasification means during operation of the pressure pulse generator, not
can it be circulated through a cooling system in the manner disclosed by
European Application 0 265 741, corresponding to U.S. Pat. No. 4,977,888.
Degasification is desirable for removing gases dissolved in the acoustic
propagation medium to prevent the formation of gas bubbles, which degrade
the propagation of the pressure pulses. Cooling of the propagation medium
is also desirable because a large amount of heat is dissipated during
operation of the pressure pulse source, which must be eliminated in order
to protect the pressure pulse source against premature failure due to
elevated operating temperatures, primarily failure of the membrane which
is subjected to high mechanical stresses.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a pressure pulse
generator of the type having a concussively driven membrane having a
simple and economical structure which permits cooling and degasification
of the acoustic propagation medium while still maintaining the capability
of generating successive pressure pulses having substantially coinciding
acoustic characteristics.
The above object is achieved in accordance with the principles of the
present invention in a pressure pulse source having a concussively driven
membrane interacting with a liquid propagation medium wherein the membrane
limits a volume containing the acoustic propagation medium, the generator
having a rigid wall (i.e., a wall having sufficient mechanical strength so
as to be pressure-resistant to the extent of not significantly
transferring pressure on one side of the wall to the other side of the
wall, at the pressures which are normally expected during the operation of
the pressure pulse source) opposite and spaced from the membrane which
subdivides the volume into two sub-volumes, with an inlet for circulating
the acoustic propagation medium being disposed in one sub-volume and an
outlet for the acoustic propagation medium being disposed in the other
sub-volume. The sub-volumes are in fluid communication via a flow
restrictor, through which the acoustic propagation medium flows, having a
restrictive effect dimensioned so that the acoustic propagation medium
contained in the sub-volume disposed between the wall and the membrane is
maintained at a static pressure sufficient to effect return of the
membrane to its initial position after it has been driven. The static
pressure is higher than the ambient pressure.
Although the return of the membrane to its initial position in the pulse
generator disclosed herein ensues by maintaining the acoustic propagation
medium adjacent the membrane at an elevated pressure in comparison to the
ambient pressure, the propagation medium is nonetheless circulated and, in
preferred embodiments of the invention, can flow through a cooling unit
and/or a degasification means. The pressure which prevails in the
sub-volume between the membrane and the wall, which causes return of the
membrane to its initial position, can be adapted to the particular
requirements dependent on the flow (volume conveyed per time unit) of the
acoustic propagation medium by selecting the restrictive effect of the
flow restrictor, such as by varying the dimensions thereof, to achieve the
desired pressure in the sub-volume situated between the between the
membrane and the wall.
In a further embodiment of the invention, the restrictive effect of the
flow restrictor can be variable, which can be achieved, for example, by
the flow restrictor being in the form of an adjustable flow control valve.
Dependent on the stiffness of the membrane, an elevated pressure which is
only slightly higher than the ambient pressure is sufficient for returning
the membrane to its initial position, for example, the elevated pressure
may be on the order of magnitude of less than 1 bar. Even if a large flow
of the acoustic propagation medium is circulated, as is preferable, for
cooling and degasification of the acoustic propagation medium, it is still
possible to maintain the pressure in the sub-volume between the membrane
and the wall at a level sufficient to return the membrane to its initial
position. Preferably, the inlet for circulating the propagation medium
discharges into the sub-volume disposed between the membrane and the wall,
so that the acoustic propagation medium is maintained at the elevated
pressure only at a location which is necessary to achieve the
aforementioned desired effect.
A further embodiment of the flow restrictor may be at least one conduit
having a suitable cross section connecting the two sub-volumes in fluid
communication. In practical embodiments of the invention, the wall is
provided with at least one bore forming the flow restrictor, or
alternatively at least one gap forming the flow restrictor can be present
between the aforementioned wall and a neighboring component part.
In a preferred embodiment of the invention, the wall is shaped as an
acoustic lens. This is particularly advantageous if the pressure pulses
emanating from the membrane require focusing, and thus an acoustic lens
will have to be provided in any event.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a longitudinal sectional view of a shockwave generator
constructed in accordance with the principles of the present invention.
FIGS. 2, 3 and 4 are enlarged sectional views of a portion of the apparatus
of FIG. 1, respectively showing different embodiments of a flow restrictor
constructed in accordance with the principles of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
A pressure pulse generator constructed in accordance with the principles of
the present invention is shown in FIG. 1 in the form of a shockwave
generator for disintegrating calculi in the body of a patient. This
shockwave generator has a tubular housing 1 with an end closed by an
electromagnetic shockwave source, generally referenced 2, and an opposite
end closed by a flexible coupling membrane 3. The shockwave source 2 has a
coil arrangement in the form of a flat coil 5 arranged on a planar seating
surface of a coil carrier 4. The flat coil 5 has terminals 6 and 7
connected by the spiral turns of the flat coil 5, one of these turns being
referenced 8. The coil carrier 4 consists of electrically insulating
material, for example aluminum oxide ceramic. The space between the turns
of the coil 5 is filled with an electrically insulating casting resin. The
terminals 6 and 7 are connected to a high-voltage pulse generator 9. The
volume limited by the housing 1, the shockwave source 2 and the coupling
membrane 3 is filled with a liquid acoustic propagation medium, for
example water.
A circular disc-shaped, planar membrane 11 is disposed on that side of the
flat coil 5 facing away from the coil carrier 4, with an insulating foil
10 disposed between the membrane 11 and the coil 5. The membrane 11
consists of electrically conductive material, for example copper. The
membrane 11, the insulating foil 10 and the coil 5 are combined with the
coil carrier 4 by means of a centering edge of the coil carrier 4 so as to
form a unit. This unit is pressed against a shoulder 13, provided in the
bore of the housing 1, by a ring 12 which presses against the coil carrier
4 and by a plurality of screws (only the center lines of two screws being
shown with dashed lines).
The side of the membrane 11 facing away from the coil 5, which is adjacent
to the acoustic propagation medium, is held against the shoulder 13 in
liquid-tight fashion, possible with the use of suitable sealants (not
shown).
A plano-concave acoustic lens 14 consisting of, for example, polystyrol, is
disposed in the bore of the housing 1 opposite that side of the membrane
11 facing away from the coil 5, with its planar side facing toward the
membrane 11. The positive lens 14 lies against that side of the shoulder
13 facing away from the membrane 11, and is axially fixed by a
schematically-indicated retainer ring 15, and is pressed into the bore of
the housing 1. The positive lens 14 thus subdivides the volume limited by
the housing 1, the shockwave source 2 and the coupling membrane 3 into two
sub-volumes. These sub-volumes are connected to each other by a flow
restrictor in form of a pipe or hose line 16. Water is supplied to the
shockwave generator through an inlet 17 which discharges into the
sub-volume situated between the membrane 11 and the positive lens 14.
Water flow is created through the line 16 into the sub-volume situated
between the positive lens 14 and the coupling membrane 3 so that a volume
of water corresponding to the water volume supplied through the inlet 17
is discharged through an outlet 18 leading from the latter sub-volume.
The outlet 18 and the inlet 17 via an outlet line 19 and an inlet line 20
between which a circulating pump 21, a cooling unit 22 and a
degasification unit 23 are connected. The pressure which is present in the
sub-volume between membrane 11 and positive lens 14 is dependent on the
difference in pressure between the inlet 17 and the outlet 18, the
magnitude of the water flow, and the restrictive effect of the line 16. As
is known, the restrictive effect of the line 16 is substantially dependent
on the length and the cross section of the line 16, and is also dependent
on the nature of the surface of the interior wall of the line 16. Thus the
aforementioned parameters can be easily selected so that not only is the
elevated pressure required for returning the membrane 11 after generating
a shockwave maintained in the sub-volume between the membrane 11 and the
positive lens 14, but also a flow sufficient for proper cooling and
degasification of the water is maintained.
Shockwaves are generated in a known manner with the shockwave generator
described above, by charging the flat coil 5 with a high-voltage pulse
from the high-voltage pulse generator 9. In response thereto, a magnetic
field is generated by the flat coil 5 extremely quickly, which induces a
current in the membrane 11 flowing in a direction opposite to the current
flowing through the coil 5. The current in the membrane 11 is also
accompanied by a magnetic field, this magnetic field being opposite in
direction to the magnetic field associated with the coil 5. As a
consequence of the repulsion forces generated by these oppositely directed
fields, the membrane 11 is concussively moved rapidly away from the flat
coil 5. As a result, a pressure pulse, which is initially planar, is
introduced into the water contained in the sub-volume adjacent the
membrane 11. This pressure pulse is focused onto a focal zone F by means
of the positive lens 14 (as indicated with dot-dash lines in FIG. 1) onto
a focal zone F which lies on the center axis M of the shockwave generator.
The focused pressure pulse propagates in the water contained in the other
sub-volume. Using the coupling membrane 3 with the assistance of a
conventional locating system, for example an x-ray locating system, the
shockwave generator is pressed against the body of a patient 24 to be
treated, in such a position that the calculus K to be disintegrated, for
example a stone in the kidney N, is located in the focal zone F. The
calculus K can be disintegrated into fragments by means of a series of
pressure pulses, the fragments being so small that they can be eliminated
naturally. The pressure pulses emanating from the membrane 11 gradually
intensify along their path through the propagation medium (water) situated
in the two sub-volumes as well as through the body tissue of the patient
24 to form shockwaves, such shockwaves being pressure pulses with an
extremely steep leading front.
As a consequence of the fact that the water contained in the sub-volume
between the membrane 11 and the positive lens 14 is maintained at an
elevated static pressure in comparison to the ambient pressure, it is
assured after a pressure pulse has been generated that the membrane 11
will be returned to its initial position, wherein it lies flush against
the surface of the flat coil 5, with the insulating foil 10 interposed
therebetween. This insures that successively generated shockwaves will
have the same acoustic characteristics. Moreover, since the acoustic
propagation medium (water) is conveyed through the cooling unit 22 and
through the degasification unit 23 by means of the circulating pump 21, it
is assured that the water is cooled and degasified in the necessary
manner. The cooling action of the cooling unit 22 is preferably such that
the water supplied to the pressure pulse generator via the inlet 17 during
normal operation has a temperature on the order of magnitude of the body
temperature of the patient 24, so as to minimize discomfort to the
patient. Moreover, as a consequence of the cooling and degasification of
the water, a premature failure of the shockeave source 2, particularly a
failure of the membrane 11, due to excessively high operating temperatures
and disturbances in the propagation of the generated shockwaves by gas
bubbles, is avoided.
One version for the flow restrictor constructed in accordance with the
principles of the present invention is shown in FIG. 2. The flow
restrictor in this embodiment is formed by a flow control valve 25
disposed in a line 26 which connects the two sub-volumes of the shockwave
generator in fluid communication. The cross section of the line 26 is
preferably (but not necessarily) dimensioned so that the flow restricting
effect of the line 26 is negligible in comparison to that of the flow
control valve 25. As shown, the restrictive effect of the flow control
valve 25 is adjustable, so that the elevated pressure present in the
sub-volume between the membrane 11 and the positive lens 14 is variable.
Another embodiment of a flow restrictor is shown in FIG. 3. In this
embodiment, the flow restrictor is formed by a bore 27 in the positive
lens 14, connecting the two sub-volumes in fluid communication. The bore
27 is dimensioned in terms of its length, diameter, etc., so that the
necessary flow restriction for creating an elevated pressure which returns
the membrane 11 to its initial position is achieved. It is also possible
to provide a plurality of bores 27, with the combined, total restrictive
effect of these bores being similarly dimensioned to achieve the necessary
elevated pressure for returning the membrane 11 to its initial position.
In the embodiment of FIG. 4, the flow restrictor is formed by a gap between
the outer edge of the positive lens 14 and the interior surface of the
housing 1. The positive lens 14 has an outer surface provided with a
continuous, substantially axially proceeding channel 28, which discharges
into a continuous slot 29 of the shoulder 13, the slot 29 also proceeding
substantially axially. The restrictive effect of this gap is essentially
dependent on the geometry thereof, which is selected to achieve the
necessary elevated pressure for returning the membrane 11 to its initial
position. The retainer ring 15 also has a slot disposed in the region of
this gap.
Some pressure pulse generators do not require a positive lens. Such
generators may be used to generate unfocused pressure pulses for
applications wherein focused pressure pulses are not needed. In other
types of pressure pulse generators having no positive lens, the membrane
is shaped in such a manner, for example spherically curved, so that the
pressure pulses emanating from the membrane are already focused. In such
pressure pulse generators which do not have a positive lens, a flat wall
having opposite end faces in parallel planes is provided instead of the
positive lens 14 shown in the embodiments of FIGS. 1 through 4.
Although the invention has been described herein in the context of the
example of a shockwave generator for medical purposes, the inventive
concept disclosed herein can also be employed in other pressure pulse
generators. Moreover, the inventive concept disclosed herein can be
employed in pressure pulse generators wherein the membrane is driven in
some manner other than electromagnetically.
Although further modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody within
the patent warranted hereon all changes and modifications as reasonably
and properly come within the scope of his contribution to the art.
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